Fluid working machines include fluid-driven and/or fluid-driving machines, such as pumps, motors, and machines which can function as either a pump or as a motor in different operating modes. Although the invention will be illustrated with reference to applications in which the fluid is a liquid, such as a generally incompressible hydraulic liquid, the fluid could alternatively be a gas.
When a fluid working machine operates as a pump, a low pressure manifold typically acts as a net source of fluid and a high pressure manifold typically acts as a net sink for fluid. When a fluid working machine operates as a motor, a high pressure manifold typically acts as a net source of fluid and a low pressure manifold typically acts as a net sink for fluid. Within this description and the appended claims, the terms “high pressure manifold” and “low pressure manifold” refer to manifolds with higher and lower pressures relative to each other. The pressure difference between the high and low pressure manifolds, and the absolute values of the pressure in the high and low pressure manifolds will depend on the application. For example, the pressure difference may be higher in the case of a pump which is optimised for a high power pumping application than in the case of a pump which is optimised to precisely determine the net displacement of fluid, for example, which may have only a minimal pressure difference between high and low pressure manifolds. A fluid working machine may have more than one low pressure manifold.
Fluid working machines are known which comprise a plurality of working chambers of cyclically varying volume, in which the displacement of fluid through the working chambers is regulated by electronically controllable valves, on a cycle by cycle basis and in phased relationship to cycles of working chamber volume, to determine the net throughput of fluid through the machine. For example, EP 0 361 927 disclosed a method of controlling the net throughput of fluid through a multi-chamber pump by opening and/or closing electronically controllable poppet valves, in phased relationship to cycles of working chamber volume, to regulate fluid communication between individual working chambers of the pump and a low pressure manifold. As a result, individual chambers are selectable by a controller, on a cycle by cycle basis, to either displace a predetermined fixed volume of fluid or to undergo an idle cycle with no net displacement of fluid, thereby enabling the net throughput of the pump to be matched dynamically to demand. EP 0 494 236 developed this principle and included electronically controllable poppet valves which regulate fluid communication between individual working chambers and a high pressure manifold, thereby facilitating the provision of a fluid working machine functioning as either a pump or a motor in alternative operating modes. EP 1 537 333 introduced the possibility of part cycles, allowing individual cycles of individual working chambers to displace any of a plurality of different volumes of fluid to better match demand.
Fluid working machines of this type require rapidly opening and closing electronically controllable valves capable of regulating the flow of fluid into and out of a working chamber from the low pressure manifold, and in some embodiments, the high pressure manifold.
Fluid working machines of this type are typically modular, permitting various components to be assembled and disassembled, for example for maintenance or replacement of worn parts. Furthermore, it is advantageous for parts or modules or assemblies which most frequently need to be replaced or repair, to be accessible without substantial disassembly of the fluid working machine as a whole.
FIG. 1 is a schematic diagram of a fluid working machine of the general type discussed above, shown generally as 200, incorporating the illustrated valve assembly 202 as a high pressure valve, which regulates the flow of hydraulic fluid between a high pressure manifold 204 and a working chamber 206. The working chamber is defined by the interior of a cylinder 208 and a piston 210 which is mechanically linked to the rotation of a crankshaft 212 by a suitable mechanical linkage 214, and which reciprocates within the cylinder to cyclically vary the volume of the working chamber. A low pressure valve 216 regulates the flow of hydraulic fluid between a low pressure manifold 218 and the working chamber. The example fluid working machine includes a plurality of working chambers and mechanically linked to the rotation of the same crankshaft, with appropriate phase differences. A shaft position and speed sensor 220 determines the instantaneous angular position and speed of rotation of the shaft, and transmits shaft position and speed signals to a controller 222, which enables a controller to determine instantaneous phase of the cycles of each individual working chamber. The controller is typically a microprocessor or microcontroller which executes a stored program in use. The low pressure valve is electronically actuatable, and the opening and/or the closing of the high and low pressure valves is under the active control of the controller.
The example fluid working machine is operable to function as either a pump or a motor in alternative operating modes. When operating as a pump, low pressure fluid is received from the low pressure manifold, and output through the high pressure valve to the high pressure manifold. Shaft power is therefore converted into fluid power. When operating as a pump, high pressure fluid is received from the high pressure manifold, and output through the low pressure valve to the low pressure manifold. Fluid power is therefore converted into shaft power.
The controller regulates the opening and/or closing of the low and high pressure valves to determine the displacement of fluid through each working chamber, on a cycle by cycle basis, in phased relationship to cycles of a working chamber volume, to determine the net throughput of fluid through the machine. Thus, the fluid working machine operates according to the principles disclosed in EP 0 361 927, EP 0 494 236, and EP 1 537 333, the contents of which are incorporated herein by virtue of this reference.
Known cylinder assemblies for machines of this type have poppet valves, for example low and high pressure face sealing valves, such as poppet valves, located at the end of the cylinder furthest from the cam which drives the pistons. It is known for one of these face sealing valves, for example the high pressure valve (which regulates the flow of fluid between the cylinder and the high pressure manifold) to be an annular valve. This may be advantageous in some circumstances as it potentially allows relatively high flow rates. However, an annular valve located at the end of the cylinder further from the cam consumes a significant amount of volume, and so limits the extent to which the cylinder assembly can be compact. Thus, the invention addresses the technical problem of providing a compact cylinder assembly including an annular valve.
Furthermore, high rates of wear are known to occur at various parts of a fluid working machine, including certain parts associated with each working chamber; the cylinder (due to motion of the piston in use), the valves and the valve members. Therefore, these parts must be provided with increased strength and/or hardness so as to reduce the rate of wear. In known fluid working machines, one or more of these parts are either incorporated into a cylinder block or are difficult to access. For example for “monoblock” machines (such as the combustion engine shown in U.S. Pat. No. 6,158,402, or the pump of US 2007/0071614), the cylinder head (or crank case) and cylinder block are combined into one casting. Thus, wear of one or more of the cylinder or the valve seats requires replacement of the entire cylinder head or crank case (as the case may be) which is time consuming and expensive.
Even where certain parts may be made relatively easily accessible and replaceable (for example the valve members of the pump of US 2007/0071614) such ease of access is provided at the expense of economy of space, such that a multi-cylinder fluid working machine having such configuration is restricted in terms of geometry or minimum overall size.
Alternatively, the disassembly of the various components may be possible but extremely time consuming. For example, the hydraulic brake pump of U.S. Pat. No. 5,562,430 (for which the high pressure valve seat is part of a sub assembly, the low pressure valve seat and piston are part of a second sub assembly and wherein the sub assemblies installed within a body) requires substantial disassembly of the pump element in order to access the high pressure valve member or high pressure valve seat.
The cylinder assembly and cylinder body of the present invention are of particular benefit in connection with fluid working machines of this type and overcome the disadvantages of known fluid working machines mentioned above.